The overall objective of the proposed research program is the development, validation and standardization of a comprehensive noninvasive radionuclide assessment of acute myocardial infarction (MI) allowing sequential quantitative study during both the immediate MI phase and a subsequent follow-up period. Studies involve a multiradionuclide approach of imaging intracellular thallium-201 and pyrophosphate distributions and radionuclide global and regional ventricular performance studies. Sequential computerized thallium-pyrophosphate imaging during the initial 72 hours of MI will be used to initially define infarct size and location for subsequent patient categorization, and will be compared to creatine kinase MI size and follow-up exercise perfusion imaging. Radionuclide imaging markers of reversible ischemia will be evaluated. Animal models will be used to validate and further define MI estimates, and define the intrinsic effects of pharmacologic agents and left ventricular hypertrophy on thallium imaging and uptake kinetics in normal and ischemic states. Tomographic scanning of experimental MI will be explored. The sole use of intracellular radionuclide distributions will not provide all the essential information required for a) serially following the patient during the first hours of MI and b) following the long term effects of therapy. To obtain this information radionuclide first pass and ECG gating ventricular function studies of regional and global left and right ventricular performance will be performed. Patients will be studied serially with both ventricular function techniques during the first day (s) of MI as well as during follow-up. Six months following MI patients will be evaluated not only at rest but also with a) exercise stress and b) nitroglycerin. Regional and global ventricular function will be specifically related to thallium and pyrophosphate infarct patterns. We will also study modifications in computer programming and instrumentation which should allow improvement in data acquisition and analysis. A major goal is a quantitative, relatively operator-independent, measure of regional ventricular performance.